If the third term of an a.p is 5 and the ratio of its 6th term to the 10th term is 7:13 , then find the sum of first 20 terms of this A.p.
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a+2d=5 ...1
a+5d/a+9d=7/13...2 on solving it u got a=3d
putting value of a in equations 1st u got d=1
and a=3 and apply sum of series u got ans 250
a+5d/a+9d=7/13...2 on solving it u got a=3d
putting value of a in equations 1st u got d=1
and a=3 and apply sum of series u got ans 250
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